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Specification defines the overall format of these services, in most cases 
their meaning and service data are object-specific or vendor-specific. 
Unless your device requires such services and documents them in detail, 
you probably do not need them for your application.

You need the following information to use the 

ncWriteDnetExplMsg

 and 

ncReadDnetExplMsg

 functions for a given explicit messaging service:

•

The class and instance identifiers for the object to which the service 
will be directed.

•

The service code used to identify the service.

•

The length and format of service request and response data. Some of 
data formats are defined by the service’s overall specification (such as 
in Appendix G, DeviceNet Explicit Services, in the DeviceNet 
Specification manual), but many data formats are object-specific or 
vendor-specific. For example, for the Reset service, Appendix G 
defines the service’s code for use with any object, but its actual data 
format is defined in the specification for the Identity Object.

•

The error codes that can be returned in the service response. Error 
codes that are common to all services can be found in Appendix H, 
DeviceNet Error Codes, in the DeviceNet Specification manual, but 
many error codes are specific to the service, object, or vendor.

As with the 

ncGetDnetAttribute

 and 

ncSetDnetAttribute

 

functions, the service data formats for the request and response are 
specified in terms of DeviceNet data types. These DeviceNet data types are 
converted to/from the data types of your programming environment (C or 
LabVIEW) as discussed in previous sections.

This section describes techniques you can use to efficiently implement an 
application that communicates with a large number of DeviceNet devices. 
In such an application, there might be only one call to 

ncOpenDnetIntf

 

(only one network), but there are usually multiple calls to 

ncOpenDnetIO

 

(and possibly 

ncOpenDnetExplMsg

).

If the configuration parameters used with 

ncOpenDnetIO

 tend to change 

over time, you might want to organize them in data structures instead of 
using constants.